The present invention relates to electrical connectors and, in particular, to electrical connectors with an improved conductor holding ability for securing a stranded electrical conductor.
Electrical connectors are commonly used to terminate an electrical conductor for the purpose of connecting the connector to an electrical device or to a different electrical conductor. A conventional electrical connector generally comprises a solid electrically-conductive metal body adapted to contact the conductor, a clamping mechanism that secures a surface of the conductor against a surface of the connector body, and means for connecting the connector to another conductor or electrical device. The ability of the electrical connector to resist disconnection of the conductor, such as pull-out of the end of a stranded conductor from within a connector-receiving bore provided in the connector body is proportional to the magnitude of the binding force applied by the clamping mechanism to the conductor.
One known type of electrical connector comprises a metal body having a cylindrical conductor-receiving bore oriented perpendicular to a threaded bore that receives a binding screw. The tip of the binding screw impales and compressively engages the end of the conductor inserted in the conductor-receiving bore to complete the electrical and mechanical connection between the connector and the conductor.
Electrical connectors will typically be rated with a recommended binding screw installation torque for a specific application and conductor size. A stranded conductor comprises a plurality of individual strands of a metal, usually aluminum or copper. Strands are arranged as a bundle in generally concentric, annular layers. The bundle of annular layers may be compacted to reduce or substantially eliminate the empty spaces (i.e., interstices) between adjoining strands.
Electrical connectors have been proposed with purportedly improved conductor-holding ability for stranded conductors. For example, the electrical connector shown in U.S. Pat. No. 4,146,290 (Annas et al.) incorporates a single, small, off-center circular window formed into the lower portion of one or more side walls thereof. A binding force is applied by tightening a binding screw received in a threaded bore in an upper wall. If the magnitude of the binding force is sufficiently large, the bottom portion of the conductor within the conductor-receiving bore may deform laterally and partially occupy the opening defined by each circular window.
Conventional electrical connectors of the foregoing type fail to consistently achieve satisfactory conductor-holding ability and have only a limited resistance to pull-out when, for example, the conductor is subjected to enormous overcurrents, such as 200,000 amps. Even if a recommended installation torque is applied to the binding screw, the conventional electrical connector may not securely fasten the conductor for the range of operating conditions or for extraordinary events or environments, particularly overcurrents of the noted magnitude.
The industry has proposed certification standards that require the electrical connector to attain specific mechanical and electrical specifications under various operating environments. Many conventional electrical connectors fail to consistently achieve the mechanical and electrical specifications under these standards. Under certain circumstances, the electrical connector may mechanically fail under a recommended installation torque that complies with a certification standard.
Thus, what is ideally desired is an electrical connector for use with a stranded conductor that tolerates large binding forces and exhibits enhanced conductor-holding ability and superior resistance to conductor pull-out when subjected to large instantaneous overcurrents.
The present invention addresses these and other problems associated with the prior art by defining an electrical connector having significantly improved mechanical holding properties. In accordance with the principles of the present invention and according to the described embodiments, the present invention is directed to an electrical connector with one or more integral structures designed to promote the improved mechanical holding ability. An electrical connector having features of the present invention comprises an electrically-conductive metal body having a conductor-receiving bore, a threaded screw-receiving bore that accommodates a binding screw having a particularized structure, and structure incorporated into the walls of the connector body that supplements the binding forces imparted by the binding screw.
In one aspect of the present invention, the connector wall structure comprises one or more slots, preferably non-circular, that are strategically positioned in opposed side walls of the connector body and communicate with both of the conductor-receiving and screw-receiving bores. When a sufficient compressive force is applied by the binding screw to deform and displace strands of a stranded conductor received within the conductor-receiving bore, each slot receives one or more strands of the conductor which are outwardly deflected. Each slot is substantially centered and substantially symmetrical with respect to the longitudinal axis of the binding screw and preferably substantially identically configured. Further, the major axis of each slot is substantially parallel to the axis of the screw-receiving bore and has a length approximately equal to the major dimension of the conductor-receiving bore measured parallel to the axis of the screw-receiving bore. In a preferred embodiment, the slots have an oval cross-sectional profile comprising a semicircular top portion, a substantially rectangular middle portion, and a semicircular bottom portion. However, the slots may have other cross-sectional profiles or serrations.
In another aspect of the present invention, the wire binding screw has a conical tip that is adapted to preferentially deflect strands of the conductor thereabout. The conical tip preferably has a blunt extremity formed with a small radius that can penetrate between and separate strands of the conductor when urged thereagainst. The conical tip has an included angle xcfx86 chosen so that strands will preferentially slide along the inclined surface thereof, forcing some strands to occupy the opening defined by each slot. These displaced strands will extend outwardly of the normal circumference of the stranded conductor and protrude into the slot beyond the diameter of the conductor-receiving bore.
The present invention has an advantage in that a conductor clamped in the conductor-receiving bore is more resistant to pull-out than heretofore believed possible. The significant displacement of the strands into the appreciably sized slots provides significant mechanical anchoring unachieved by conventional electrical connectors.
The present invention has a further advantage that the current-carrying capability of the connection is enhanced. The slots have sharp edges that scrape oxidation from surfaces of the outer strands to enhance the electrical contact between the conductor and body of the electrical connector.
The present invention has a yet further advantage that the overall design of the connector body enhances the torque that can be applied to the binding screw. As a result, a larger binding force may be applied by the tip of the binding screw to the surface of the conductor, enhancing pull-out resistance of the conductor relative to the connector.
These and other objects, advantages, features, and embodiments will be apparent with reference to the following drawings and detailed written description.